Multiple Column Processes

While multi-product columns could be used to separate mixtures into products with distinct compositions, sharper separations usually require processing with multiple columns to achieve the desired splits and purities. A possible scheme would be to break down the separation process into a forward flowing series of single-feed, two-product distillation columns, each of which makes the separation between two key components. In a more complex multi-column approach, the process may include recycle streams, external separation-enhancing streams, stream splits, recombination of streams, energy integration, and so on, all aimed at achieving an economic optimum. 

For processes belonging to this category and involving only single-feed, two-product distillation columns, a single sequence exists for separating a binary  

That is, the mixture AB is fed to a distillation column the lighter component, 

Two columns are needed in either of these sequences the first to recover one of the components in the ternary and the second to separate the remaining two. For a four-component mixture, five altemative sequences could be used, each requiring three distillation columns  

Sequences could be listed in this manner for any number of components. 

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The separations that cannot be achieved in a single column are carried out in multiple columns, frequently interconnected in various complex configurations aimed at optimizing the process while meeting the separation specifications. Multiple column processes are also discussed in this chapter. 

Chapter 9 Complex Distillation and Multiple Column Processes... 

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